- Best Buy will offer you $150 minimum for an iPhone 4S in “Good” condition.

- An iPhone 5 on-contract costs $199, but Best Buy currently offers a separate $50 off iPhone 5 campaign, so, before taxes and such, these programs combined can yield about $200 off of an iPhone 5 purchase.

The program will launch in stores tomorrow, but the company will begin heavily promoting it in its Sunday ads. The special will run for 9 days after tomorrow. It just so happens that Best Buy’s currently running $50 iPhone 5 special runs until June 29th as well.

The program does have some caveats:

Only Verizon, AT&T, and Sprint iPhones are covered (no T-Mobile)

The specials are exclusive to Best Buy retail stores

If your phone is worth more than $150, the difference will be applied to a gift card, not a higher-end iPhone 5 model.

Definitely a solid deal for heavily used, less desirable models (Sprint, Verizon), but be sure to check other trade-in services before heading into a Best Buy store. For instance, Gazelle will pay you $215 for a 64GB iPhone 4S AT&T (good condition), plus another $10 if you use the special 9toToys promo. In some cases, Amazon will pay upwards of $300 for an iPhone 4S. Per usual, selling privately (eBay, Craigslist, etc) generally yields the highest payout but requires the most time and effort. Make sure you survey all of your options before jumping into bed with Best Buy.